Comparison Among Epifaunal Assemblages Associated With
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Comparison of epifaunal assemblages between Cymodocea nodosa and Caulerpa prolifera meadows in Gran Canaria (eastern Atlantic) Lydia Png González Máster en Oceanografía Universidad de Las Palmas de Gran Canaria Director: Dr. Fernando Tuya Cortés Tutor: Dr. Santiago Hernández León Julio 2013 Comparison of epifaunal assemblages between Cymodocea nodosa and Caulerpa prolifera meadows in Gran Canaria (eastern Atlantic) Lydia Png-Gonzalez1*, Maite Vázquez-Luis2, Fernando Tuya1 1Centro en Biodiversidad y Gestión Ambiental, Marine Sciences Faculty, Campus Tafira, Universidad de Las Palmas de Gran Canaria, 35017 Tafira, Las Palmas, Spain 2Instituto Español de Oceanografía, Centro Oceanográfico de Baleares. Muelle de Poniente s/n, 07015 Palma de Mallorca, Spain 1 ABSTRACT Epifaunal invertebrates are sensitive to changes in the identity of the dominant host plant, so assessing differences in the diversity, abundance and structure of epifaunal assemblages is particularly pertinent in areas where seagrasses have been replaced by alternative vegetation (e.g. green seaweeds). In this study, we aimed to compare the diversity, abundance and structure of epifaunal assemblages, with particular emphasis on amphipods, between meadows dominated by Cymodocea nodosa and the green algae Caulerpa prolifera on shallow soft bottoms of Gran Canaria Island, determining whether patterns were temporally consistent. The epifaunal assemblage structure (abundance and composition) consistently differed between both plants, being more diverse and abundant epifaunal assemblages associated with C. prolifera- dominated beds than those inhabiting C. nodosa meadows. Amphipods constituted ca. 70% of crustaceans for the overall study, including 37 species belonging to 16 families. The amphipods abundance recorded was ca. 3 times larger in C. prolifera-dominated beds (1248.13 ± 136.83 ind. m-2, mean ± SE) than in C. nodosa meadows (396.88 ± 77.36 ind. m-2). Multivariate analysis of the community showed significant differences between habitats, with a clear segregation of the species. For instance, Microdeutopus stationis, Dexamine spinosa, Aora spinicornis, Ischyrocerus inexpectatus and Apherusa bispinosa were more abundant in C. prolifera-dominated beds; while the new genus, new species of caprellid, Mantacaprella macaronensis, dominated in C. nodosa meadows. However, some species such as Pseudoprotella phasma and Ampithoe ramondi were found without significant differences in both habitats. Keywords: Amphipoda, epifauna, assemblage structure, ecosystem services, seagrass, Canary Islands. 2 1. Introduction On subtidal soft bottoms, seagrasses form one of the most productive ecosystems worldwide, providing high-value ecosystem services such as delivery of food and habitat for a wide range of organisms (Costanza et al., 1997; Duffy, 2006; Thomsen et al., 2012), support of commercial fisheries, nutrient cycling, sediment stabilization and sequestration of carbon (Duarte et al., 2000; Waycott et al., 2009). Seagrasses, and the services they provide, are, however, threatened by impacts derived from coastal development and growing human population, as well as by impacts caused by climate change (Duarte, 2002; Orth et al., 2006; Waycott et al., 2009). Conservation of these valuable habitats is, therefore, important, particularly since seagrass meadows are declining worldwide, mainly in areas of intense human activities (Hughes et al., 2009). Cymodocea nodosa (Ucria) Ascherson is a seagrass distributed across the Mediterranean Sea and adjacent areas of the Atlantic Ocean, including the Macaronesian archipelagos of Madeira and the Canaries (Reyes et al., 1995; Tuya et al., 2012). Meadows constituted by C. nodosa are the dominant vegetated communities on shallow soft substrates throughout the Canary Islands (Pavón-Salas et al., 2000; Barberá et al., 2005; Monterroso et al., 2012), where they provide food and shelter for diverse invertebrate and fish assemblages, including a ‘nursery’ habitat for larval and juvenile fish stages (Tuya et al., 2006; Espino et al., 2011a, 2011b). However, C. nodosa meadows are severely decreasing at local scales, as a result of a range of human- mediated impacts (Martínez-Samper, 2011; Tuya et al., 2013). In these coastal areas, the decline of C. nodosa seagrass meadows often results in the replacement by 3 opportunistic green algae of the genus Caulerpa, Caulerpa prolifera (Forsskål) J.V. Lamouroux in particular (Martínez-Samper, 2011; Tuya et al., 2013). Caulerpa prolifera is a native seaweed in the Canary Islands (Haroun et al., 2003), forming extensive beds on soft bottoms in waters from ca. 5 to 50 m depth. Several Caulerpa species contain caulerpenyne, a major secondary metabolite, which varies depending on the species, locations and seasons (Jung et al., 2002; Box et al., 2010), and appears to possess toxic and feeding deterrent properties against faunal herbivores (Smyrniotopoulos et al., 2003). Caulerpenyne may also act as an antimitotic substance, preventing settlement of most epiphytes (Sánchez-Moyano et al., 2001a). In addition, the high sediment-retention capacity of Caulerpa beds induces organic enrichment (Hendriks et al., 2010), potentially altering the distribution and abundance of associated animal populations (Sánchez-Moyano et al., 2001a). When seagrasses are replaced by seaweeds, the quantity and quality of habitat for associated faunal assemblages may be altered, as well as flows of energy and matter through the ecosystem (Thomsen et al., 2012). In particular, epifaunal invertebrates are sensitive to changes in plant abundance and structure (e.g. through plant attributes such as plant size, biomass, shoot density, etc.), so differences in the diversity, abundance and structure of invertebrate assemblages are expected between different types (identities) of vegetation within the same geographical and environmental context (Sirota and Hovel, 2006). The aim of this study was to compare the diversity, abundance and structure of epifaunal assemblages between meadows dominated by Cymodocea nodosa and Caulerpa prolifera on shallow soft bottoms of Gran Canaria Island, determining whether patterns were temporally consistent. Particular emphasis was concentrated on amphipod assemblages, since amphipods are one of the most quantitatively and 4 important groups of invertebrates associated with coastal vegetated habitats, while these organisms also play an important role as trophic resources for fish populations (Sánchez-Jerez et al., 1999; Vázquez-Luis et al., 2009). In this sense, amphipods respond to habitat alterations and can, therefore, be used as an indicator of environmental impacts on vegetated habitats (Virnstein, 1987; Conradi et al., 1997; Sánchez-Jerez et al., 2000; Vázquez-Luis et al., 2008, 2009). 2. Material and methods 2.1. Study area and sampling design The study was carried out in Gran Canaria (Canary Islands, eastern Atlantic), at a range of localities across the island (Table 1) dominated by either subtidal mono- specific Cymodocea nodosa meadows or beds constituted by Caulerpa prolifera. Table 1. Sampled localities to compare epifaunal assemblages between Cymodocea nodosa seagrass meadows and Caulerpa prolifera-dominated beds at Gran Canaria Island. Habitat Locality UTM X UTM Y Depth (m) Date C. nodosa L1 421440 3080993 11.3 Nov’11 C. nodosa L2 462235 3082272 10 Nov’11 C. nodosa L1 461982 3081367 11.3 Oct’12 C. nodosa L2 462114 3082872 8.8 Oct’12 C. prolifera L1 463559 3089684 13.7 Nov’11, Oct’12 C. prolifera L2 463105 3089320 14.6 Nov’11, Oct’12 Each habitat (i.e. C. nodosa vs. C. prolifera-dominated beds) was sampled at each of two localities, where n=10, randomly allocated, samples were collected by SCUBA divers, using a 20x20 cm quadrat. Collections were performed cutting the seagrass/seaweed immediately above the sediment surface, keeping the vegetation with 5 the associated epifauna in unbleached woven cotton bags (Brearley et al., 2008; Gartner et al., 2013). Sampling was repeated twice (November 2011 and October 2012) to merely assess whether patterns in the diversity, abundance and structure of epifaunal assemblages between beds dominated by C. nodosa and C. prolifera were temporally consistent. Labelled samples were preserved in a freezer (-20 ºC) until processed. In the laboratory, samples collected were initially defrosted and subsequently sieved through a 500 m mesh to retain macrofaunal organisms. Specimens were sorted and counted into different taxonomic groups under a binocular microscope and preserved in 70% ethanol. Four main functional groups: Crustacea, Mollusca, worms (including Annelida and Sipuncula) and other fauna (Chelicerata, Chordata and Echinodermata) were considered. All organisms were identified to species level, whenever possible. In particular, amphipods were identified to the lower taxonomic resolution (species in most cases), because amphipods was the most abundant taxa and because of their importance as biological indicators of human-induced alterations (Sánchez-Jerez et al., 2000). The amount of vegetated biomass (wet weight) was obtained for each replicate to account for differences in the amount of habitat (vegetation) among samples. 2.2. Statistical analysis 2.2.1. Univariate analysis Differences in the abundance and species density (the number of species per area) of the dominant groups (here, Crustacea, Mollusca, Amphipoda, worms and other fauna) between habitats, localities within habitats and times were tested using a 3-way ANCOVA, which incorporated the factors: ‛Habitat’